June 27, 2020 – We are going to see onshore flow today with strong winds through the Delta into tonight with gusts up to 45 mph. Onshore winds will be shifting north on Sunday and will increase with breezy northerly winds expected Sunday afternoon continuing into Monday afternoon. This will bring elevated fire weather conditions to the area especially over the northern Sacramento Valley. We will see cooler temperatures today with the cooling continuing into Sunday. Temperatures will be seasonal next week.
Heights falling over interior NorCal today with increased onshore flow as upper troughing deepens along the West Coast. Strong wind funneling through the Carquinez Strait overnight will continue today, providing low level CAA inland. Forecast high temperatures expected to be around 5 to 10 degrees cooler for most areas compared to Friday.
Heights/thicknesses continue to lower Sunday as upper low moves through the PacNW into the Intermountain West. Models showing associated precip remaining mostly outside of our CWA with a few showers possible over higher elevations of the Sierra Nevada. Additional cooling expected Sunday with highs upwards of 15 degrees lower than Saturday. 80s forecast for highs in the Central Valley Sunday with 50s to 70s for the mountains and foothills.
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Upper ridging builds inland over NorCal Sunday night and Monday as EPAC surface high builds into Oregon. Breezy northerly wind develops over portions of interior NorCal during this period. Increased fire concern results, however period of breezy wind looks limited. Models suggest a slight chance of afternoon showers over our southern Sierra Nevada Monday. High temperatures rebound back up several degrees Monday, but remain below normal.
Subsidence continues to increase over interior NorCal Tuesday with additional AMS warming. Forecast guidance suggests max T’s on Tuesday will be around 2 to 5 degrees above normal. Lighter wind expected Tuesday under weaker pressure gradient.
Extended Discussion (Wednesday through Saturday)
Weak upper trough centered just off the West Coast favored by the ensembles for the second half of next week. Dry weather with slightly above average temperatures expected.